1. Field of the Invention
This invention relates to a plasma display panel(PDP), and more particularly to electrodes in the PDP and a fabrication method thereof that are capable of lowering their resistance components and fine-patterning them.
2. Description of the Related Art
Generally, a plasma display panel(PDP) radiates a fluorescent body by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. The PDP is largely classified into a direct current(DC) driving system and an alternating current(AC) driving system.
The PDP of AC driving system is expected to be highlighted into a future display device because it has advantages in the low voltage drive and a prolonged life in comparison to the PDP of DC driving system. Also, the PDP of AC driving system allows an alternating voltage signal to be applied between electrodes having a dielectric layer therebetween to generate a discharge every half-period of the signal, thereby displaying a picture. Since such an AC-type PDP uses a dielectric material, the surface of the dielectric material is charged with electricity. The AC-type PDP allows a memory effect to be produced by a wall charge accumulated to the dielectric material due to the discharge.
FIG. 1 is a sectional view showing the structure of a discharge cell in the conventional three-electrode AC-type PDP, in which a lower plate is illustrated in a state of rotating an angle of 90°. In FIG. 1, the discharge cell includes an upper plate 10 provided with a sustaining electrode pair 12 and 14, and a lower substrate 20 provided with an address electrode 20. The upper substrate 10 and the lower substrate 20 are spaced, in parallel, from each other with having a barrier rib 28 therebetween.
A mixture gas such as Ne—Xe or He—Xe, etc. is injected into a discharge space defined by the upper substrate 10 and the lower substrate 20 and the barrier rib 28. The sustaining electrode pair 12 and 14 consists of transparent electrodes 12A and 14A and metal electrodes 12B and 14B. The transparent electrodes 12A and 14A are usually made from Indium-Tin-Oxide (ITO) and has an electrode with of about 300 p.m. Usually, the metal electrodes 12B and 14B takes a three-layer structure of Cr—Cu—Cr and have an electrode width of about 50 to 100 μm. These metal electrodes 12B and 14B play a role to decrease a resistance of the transparent electrodes 12A and 14A with a high resistance value to thereby reduce a voltage drop. Any one 12 of the sustaining electrode pair 12 and 14 is used as a scanning/sustaining electrode that responds to a scanning pulse applied in an address interval to cause an opposite discharge along with the address electrode 22 while responding to a sustaining pulse applied in a sustaining interval to cause a surface discharge with the adjacent sustaining electrodes 14. A sustaining electrode 14 adjacent to the sustaining electrode 12 used as the scanning/sustaining electrode is used as a common sustaining electrode to which a sustaining pulse is applied commonly. A distance between the sustaining electrode pair 12 and 14 is set to be approximately 100 μm. On the upper substrate 10 provided with the sustaining electrode pair 12 and 14, an upper dielectric layer 16 and a protective layer 18 are disposed. The dielectric layer 16 is responsible for limiting a plasma discharge current as well as accumulating a wall charge during the discharge. The protective film 18 prevents a damage of the dielectric layer 16 caused by a sputtering generated during the plasma discharge and improves an emission efficiency of secondary electrons. This protective film 18 is usually made from MgO. The address electrode 22 is crossed with the sustaining electrode pair 12 and 14 and is supplied with a data signal for selecting cells to be displayed. On the lower substrate 20 formed with the address electrode 24, a lower dielectric layer 24 is provided. Barrier ribs 28 for dividing the discharge space are extended perpendicularly on the lower dielectric layer 24. On the surfaces of the lower dielectric layer 24 and the barrier ribs 28 is coated a fluorescent material 26 excited by a vacuum ultraviolet ray to generate a red, green, or blue visible light.
FIGS. 2A to 2E are sectional views for explaining a process of forming the sustaining electrode pair in FIG. 2 step by step. In FIG. 2A, on the upper substrate 10 are sequentially disposed a transparent electrode material layer 12A and a photosensitive resin pattern 28. The transparent electrode material layer 12A is formed on the surface of the upper substrate 10 using the sputtering technique or the vacuum vapor deposition technique. The photosensitive resin pattern 28 is provided by forming the photosensitive resin layer on the transparent electrode material layer 12A and then patterning it.
Next, the transparent electrode 12 shown in FIG. 2B is provided by taking advantage of the photosensitive resin pattern 28 to make a patterning of the transparent electrode material layer 12A under it. The photosensitive resin pattern 28 on the transparent electrode 12 is removed. After forming the transparent electrode 12, the first chrome(Cr) thin film 30, the copper(Cu) thin film 32 and the second Cr thin film 34 are sequentially disposed as shown in FIG. 2C. The first Cr thin film 30, the Cu thin film 32 and the second Cr thin film 34 are sequentially disposed on the upper substrate 10 provided with the transparent electrode 12 using the sputtering technique.
Next, as shown in FIG. 2D, the second photosensitive resin pattern 36 is provided by forming a photosensitive resin layer on the second Cr thin film 34 and thereafter patterning it. As shown in FIG. 2E, the first Cr pattern 30A, the Cu pattern 32A and the second Cr pattern 34A are provided by taking advantage of the second photosensitive resin pattern 36 to make a sequential patterning of the second Cr thin film 34, the Cu thin film 32 and the first Cr thin film 30 under it. The first Cr pattern 30A, the Cu pattern 32A and the second Cr pattern 34A provide the bus electrode 14 shown in FIG. 1. The second photosensitive resin pattern 36 on the second Cr pattern 34A is removed.
In the conventional PDP bus electrode fabrication method as described above, the sputtering technique has been used for forming the first Cr thin film 30, the Cu thin film 32 and the second Cr thin film 34. However, the sputtering method is unsuitable for a mass production because expensive vacuum equipment must be used and a deposition time is long. In the PDP, the bus electrode 14, particularly the Cr thin film, must be thickly provided so as to lower a resistance of the bus electrode 14 to increase the efficiency. To form the bus electrode 14 thickly using the conventional PDP bus electrode fabrication method has a problem in that an adhesive force is deteriorated by a stress, etc. to enlarge a resistance component and to lengthen a deposition time. For this reason, the prior art has widened a line width of the bus electrode 14 instead of 1-adjusting a thickness thereof so as to lower the resistance component. If the line width of the bus electrode 14 is wide, however, then most visible lights generated by a radiation of the fluorescent material 26 are reflected by the bus electrode 14 to deteriorate the efficiency.
Otherwise, to form the bus electrode 14 using the screen printing technique like the address electrode 22 has an advantage in that its fabrication process is simple, while having a drawback in that an organization of the electrode fails to be dense to increase the resistance component as well as to require an additional firing process. Also, it is difficult to make electrodes with a minute line width required for a fine structure using the screen printing technique. For instance, it is difficult to provide a bus electrode with a line width less than 100 μm using the screen printing technique.
Moreover, the conventional PDP bus electrode has a problem in that the Cu thin film is liable to be oxidized or to be diffused into the dielectric to thereby deteriorate a performance of the PDP device.